Salmonella and public health – what veterinarians should know

Salmonella seems to be everywhere these days.  This year in eggs (over a half-billion recalled since August); in raw pet food diets; in specialty dry dog and cat foods sold at veterinary clinics; in contaminated pet vitamins; in African dwarf frogs (sold in Hallmark and Brookstone stores neatly contained in their own Frog-o-Sphere for your desk); and even in frozen feeder rodents sold online by the tens of thousands by Mice Direct.  In past years, we’ve seen humanSalmonella outbreaks due to contaminated raw alfalfa sprouts, tomatoes, cantaloupe, peppercorns, lettuce, peanut butter; pigs’ ears and jerky pet treats …and the list goes on. 

About 40,000 cases of salmonellosis are reported to CDC annually.  But that’s just the tip of the iceberg: CDC estimates that for every reported case, thirty (30!) Salmonella infections go either undiagnosed or unreported.  And about 400 people die of acute salmonellosis every year in the U.S.  

Salmonella bacteria are carried by a huge range of animal species.  Most human cases are due to eating food contaminated by animal feces, but some cases are due to direct animal contact, especially with reptiles and amphibians, or indirect contact with contaminated fomites.  A ban on sales of small turtles (carapace < 4”) instituted in 1975 was estimated to have prevented 500,000 human Salmonella infections over the subsequent 5-year period -- however turtles and other reptiles and amphibians are increasingly popular as pets and remain a significant source of human infections.  Young poultry frequently carry Salmonella, and many outbreaks associated with spring or Easter chicks or ducklings have been documented.  Young animals such as puppies, kittens and young ruminants (especially those with diarrhea) are another source of Salmonella infection.

Human Salmonella infection linked to dry pet food

A recent report in the journal Pediatrics by Casey Barton Behravesh DVM described an outbreak of human Salmonella infections linked to contaminated dry dog and cat foods..  This was the first such outbreak documented in the scientific literature. [See Pediatrics 2010:126;477-483.  Available on-line at http://www.pediatrics.org.]

The outbreak occurred over 3 years (2006-08) before the manufacturing plant was finally permanently closed.  More than 23,000 tons of dry pet food sold under 105 brand names were recalled.  Epidemiologic analysis of 79 cases from 21 states and a case-control study evaluating risk factors revealed some important findings:

·      The outbreak was due to an unusual strain, Salmonella Schwarzengrund, which was ultimately identified in bags of the pet food, in environmental samples collected at the manufacturing plant, and in fecal samples from dogs that had been fed the implicated food

·      Human illnesses occurred over 3 years, meaning there were ongoing contamination problems at the manufacturing plant that went undetected for a long period of time

·      Almost half the illnesses were in children under 2 years of age

·      Households with sick people were almost 7 times as likely to have recently bought the implicated pet food compared to control households

·      Illness among infant case patients was 4 times more likely in households that fed their dogs in the kitchen

Pet food contamination and recalls are cause for concern

In recent years there have been numerous pet food recalls due to Salmonella contamination.  In most there were no known human (or animal) cases linked to the foods, but infections were likely to have occurred given the low rate of diagnosis and reporting of human disease. Recalls have involved commercial raw pet foods, smoked or partially-cooked pet treats, and dry foods.  It should always be assumed that raw or undercooked animal-derived pet foods or treats are a potential source of enteric pathogens such as Salmonella, E. coli, Campylobacter, Yersinia, and various parasites.  In addition, given the findings in the study published in Pediatrics, dry foods should be considered as potential sources of infection.

Studies published since 2008 have documented shedding of pathogenic bacteria by dogs fed raw meat/by product diets compared to dogs not fed raw diets.  A number of these studies specifically looked at therapy dogs. You can find a summary of these findings prepared by Dr Scott Weese on the University of Guelph Centre for Public Health & Zoonoses’ Worms and Germs Blog at  http://www.wormsandgermsblog.com.

A study by Erin Leonard DVM published this spring in Zoonoses and Public Health found 32 (23%) of 138 dogs in Ontario, Canada fed a raw meat diet were shedding Salmonella at any one time, but only 4 of the 32 had any history of diarrhea in the prior month.  This same study also reported that the sensitivity of testing a single fecal sample from an infected dog was 35.5%, emphasizing the importance of collecting multiple stool samples when culturing for Salmonella. 

Because of the concern about potential shedding of enteric pathogens, in May 2010 the Delta Society announced a new policy that prohibits animals fed a raw protein diet from participating in its Pet Partners therapy program.  This is to protect people visited by therapy animals from the potential risk, even though disease transmission by this route has not been proven. Given that therapy animal programs are visiting hospitalized patients and people at higher risk of serious illness if exposed to zoonotic pathogens, this policy seems prudent.  Learn more about the Delta Society policy at: 

http://www.deltasociety.org/Page.aspx?pid=638

New Public Health program for Salmonella prevention

Earlier this year, Public Health—Seattle & King County’s Zoonotic Disease Program and the KC Board of Health enacted new regulations for pet-related businesses including pet shops, kennels, daycares, groomers, shelters, and feed store selling baby poultry.   Among a comprehensive set of provisions, these regulations address Salmonella prevention through the following:

• Clearly visible signs must advise potential purchasers of reptiles or amphibians about Salmonella risks and that these animals are unsuitable as pets for persons with immune deficiencies or in households with children < 5 years of age
• Feed stores selling baby poultry must post signs advising of the risk of Salmonella and importance of hand washing after handling poultry
• Hand washing facilities or hand sanitizers must be provided to patrons after handling animals in pet shops or feed stores
• Infection control plans to protect employees and customers (as well as animals) are required for most types of pet businesses
•  Information about zoonotic disease prevention must be provided to customers purchasing pets (expect aquarium fish) or live poultry
• Pet food retailers selling raw or partially cooked animal-derived pet foods or pet treats must:
• Provide tongs, scoops or tissues and bags for customers to pick up pet treats (i.e., pig ears, hooves, raw hides, meaty bones, jerkies) offered for sale from open bins or baskets, to avoid bare-handed contact
• Keep open bins or baskets of high risk pet treats out of reach of young children
• Ensure that high risk pet foods are either labeled with safe handling instructions or that these instructions are provided to the customer at time of purchase or posted in the sales area
• Advise customers that people with immune deficiencies and young children should not handle potentially hazardous pet foods or treats
• Maintain refrigerators and freezers holding pet foods in good working order
• Protect foods from cross contamination by separating foods requiring freezing or refrigeration from all other types of pet foods or human foods during storage; control rodents and insect pests
• Advise customers to wash hands after handling raw or partially cooked pet foods or pet treats to help prevent illness

More information about King County’s pet business regulations and permit requirements can be found at :  http://www.kingcounty.gov/healthservices/health/ehs/petbusinesses.aspx

Veterinarians are an important source of objective information

It is important for veterinarians to keep up-to-date on zoonotic disease concerns so that they can provide the best information possible to pet owners.  Salmonella risks related to pets and pet foods is an area of great concern, and misinformation abounds. Pet owners are naturally alarmed by the media reports and frequent recalls of pet foods and should be able to turn to their veterinarians as a trusted source of objective advice on disease risks and prevention.  We hope the information in this article will assist veterinarians in this role.

For more information, see our Zoonotic Disease Program website at www.kingcounty.gov/health/zoonotics.       

-Sharon Hopkins, DVM, MPH

Public Health Veterinarian

Public Health--Seattle & King County